1. Field of the Invention
The present invention relates to the preparation of polyisobutylene (PIB). In particular the present invention relates to the preparation of highly reactive PIB having a relatively high degree of terminal unsaturation. In this latter regard, the invention provides a novel liquid phase process for the polymerization of isobutylene to prepare highly reactive PIB using a modified BF3 catalyst.
2. The Prior Art Background
The polymerization of isobutylene using Friedel-Crafts type catalysts, including BF3, is a generally known procedure which is disclosed, for example, in xe2x80x9cHIGH POLYMERSxe2x80x9d, Vol. XXIV (J. Wiley and Sons, Inc., New York, 1971), pp. 713 ff. The degree of polymerization of the products obtained varies according to which of the various known polymerization techniques is used. In this latter connection, it is to be understood that the molecular weight of the polymeric product is directly related to the degree of polymerization.
It is also known that PIB may be manufactured in at least two different gradesxe2x80x94regular and high vinylidene. Conventionally, these two product grades have been made by different processes, but both often and commonly use a diluted isobutylene feedstock in which the isobutylene concentration may range from 40-60% by weight. More recently it has been noted that at least the high vinylidene PIB may be produced using a concentrated feedstock having an isobutylene content of 90% by weight or more. Non-reactive hydrocarbons, such as isobutane, n-butane and/or other lower alkanes commonly present in petroleum fractions, may also be included in the feedstock as diluents. The feedstock often may also contain small quantities of other unsaturated hydrocarbons such as 1-butene and 2-butene.
Regular grade PIB may range in molecular weight from 500 to 1,000,000 or higher, and is generally prepared in a batch process at low temperature, sometimes as low as xe2x88x9250 to xe2x88x9270xc2x0 C. AlCl3, RAlCl2 or R2AlCl are used as catalysts. The catalyst is not totally removed from the final PIB product. Molecular weight may be controlled by temperature since the molecular weight of the product varies inversely with temperature. That is to say, higher temperatures give lower molecular weights. Reaction times are often in the order of hours. The desired polymeric product has a single double bond per molecule, and the double bonds are mostly internal. Generally speaking, at least about 90% of the double bonds are internal and less than 10% of the double bonds are in a terminal position. Even though the formation of terminal double bonds is believed to be kinetically favored, the long reaction times and the fact that the catalyst is not totally removed, both favor the rearrangement of the molecule so that the more thermodynamically favored internal double bond isomers are formed. Regular PIB may be used as a viscosity modifier, particularly in lube oils, as a thickener, and as a tackifier for plastic films and adhesives. PIB can also be functionalized to produce intermediates for the manufacture of detergents and dispersants for fuels and lube oils.
High vinylidene PIB, a relatively new product in the marketplace, is characterized by a large percentage of terminal double bonds, typically greater than 70% and preferentially greater than 80%. This provides a more reactive product, compared to regular PIB, and hence this product is also referred to as highly reactive PIB. The terms highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HV-PIB all include a reactor system, employing BF3 and/or modified BF3 catalysts, such that the reaction time can be closely controlled and the catalyst can be immediately neutralized once the desired product has been formed. Since formation of terminal double bonds is kinetically favored, short reactions times favor high vinylidene levels. The reaction is quenched, usually with an aqueous base solution, such as, for example, NH4OH, before significant isomerization to internal double bonds can take place. Molecular weights are relatively low. HV-PIB having a number average molecular weight (MN) of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization. Prior U.S. Pat. Nos. 4,152,499 dated May 1, 1979, 4,605,808 dated Aug. 12, 1986, 5,068,490 dated Nov. 26, 1991, 5,191,044 dated Mar. 2, 1993, 5,286,823 dated Jun. 22, 1992, 5,408,018 dated Apr. 18, 1995 and 5,962,604 dated Oct. 5, 1999 are directed to related subject matter.
U.S. Pat. No. 4,152,499 describes a process for the preparation of PIBs from isobutylene under a blanket of gaseous BF3 acting as a polymerization catalyst. The process results in the production of a PIB wherein 60 to 90% of the double bonds are in a terminal (vinylidene) position.
U.S. Pat. No. 4,605,808 discloses a process for preparing PIB wherein a catalyst consisting of a complex of BF3 and an alcohol is employed. It is suggested that the use of such a catalyst complex enables more effective control of the reaction parameters. Reaction contact times of at least 8 minutes are required to obtain a PIB product wherein at least about 70% of the double bonds are in a terminal position.
U.S. Pat. No. 5,191,044 discloses a PIB production process requiring careful pretreatment of a BF3/alcohol complex to insure that all free BF3 is absent from the reactor. The complex must contain a surplus of the complexing agent in order to obtain a product wherein at least about 70% of the double bonds are in a terminal position. The specification broadly suggests that reaction times ranging from 10 seconds to several hours are within the contemplation of the disclosure; however, none of the specific examples reveals the residence time employed. Moreover, there is absolutely no disclosure whatsoever in the ""044 patent which correlates reaction time with either the choice of catalyst complexing agent or the formation of terminal double bonds. Additionally, while the ""044 patent reference broadly suggests that reaction temperatures may generally be below 0xc2x0 C., in each of the specific examples, the reaction temperature is xe2x88x9210xc2x0 C. or lower. And once again there is no disclosure whatsoever in the ""044 patent which correlates reaction temperature with either the choice of catalyst complexing agent or the formation of terminal double bonds.
In addition to close control of reaction time, the key to obtaining high vinylidene levels seems to be control of catalyst reactivity. This has been done in the past by complexing BF3 with various oxygenates including sec-butanol and MTBE. One theory is that these complexes are actually less reactive than BF3 itself, disproportionately slowing the isomerization reaction and thus allowing for greater differentiation between the vinylidene forming reaction (polymerization) and the isomerization reaction rates. Mechanisms have also been proposed that suggest the BF3 complexes are non-protonated and thus are not capable of isomerizing the terminal double bond. This further suggests that water (which can preferentially protonate BF3) must generally be excluded from these reaction systems. In fact, prior publications describing preparation of PIB using BF3 complexes teach low water feed (less than 20 ppm) is critical to formation of the high vinylidene product.
HV-PIB is increasingly replacing regular grade PIB for the manufacture of intermediates, not only because of higher reactivity, but also because of developing requirements for xe2x80x9cchloride freexe2x80x9d materials in the final product applications. Important PIB derivatives are PIB amines, PIB alkylates and PIB maleic anhydride adducts.
PIB amines can be produced using a variety of procedures involving different PIB intermediates which provide a reactive site for subsequent amination. These intermediates may include, for example, epoxides, halides, maleic anhydride adducts, and carbonyl derivatives. Reference to HV-PIB as xe2x80x9chighly reactivexe2x80x9d is relative to regular grade PIB. HV-PIB is still not, in absolute terms, highly reactive toward formation of some of these intermediates. Other classes of compounds, polyethers for example, can be much more reactive in the formation of amines and amine intermediates. Amines derived from polyethers are known as polyether amines (PEA""s) and are competitive products to PIB amines.
The use of HV-PIB as an alklylating agent for phenolic compounds, is triggered by the higher reactivity and higher yields achievable with HV-PIB. These very long chain alkyl phenols are good hydrophobes for surfactants and similar products.
The largest volume PIB derivatives are the PIB-maleic anhydride reaction products. HV-PIB is reacted with maleic anhydride through the double bond giving a product with anhydride functionality. This functionality provides reactivity for the formation of amides and other carboxylate derivatives. These products are the basis for most of the lube oil detergents and dispersants manufactured today. As mentioned above, PIB-maleic anhydride products can also be used as intermediates in the manufacture of PIB amine fuel additives.
The present invention provides a novel process for the efficient and economical production of HV-PIB. Generally speaking, the invention provides a HV-PIB production process wherein the polymerization reaction takes place at higher temperatures and at lower reaction times than were thought possible in the past. In particular, the present invention provides a liquid phase polymerization process for preparing low molecular weight, highly reactive polyisobutylene. Generally speaking, the process may involve cationic polymerization. However, under some conditions the polymerization reaction may be covalent. Particularly the latter may be true when ether is used as a complexing agent. In accordance with the invention, the process includes the provision of a feedstock comprising isobutylene and a catalyst composition comprising a complex of BF3 and a complexing agent. The feedstock and the catalyst composition are introduced either separately or as a single mixed stream into a residual reaction mixture in a reaction zone. The residual reaction mixture, the feedstock and the catalyst composition are then intimately intermixed to present an intimately intermixed reaction admixture in said reaction zone. The reaction admixture is maintained in its intimately intermixed condition and kept at a temperature of at least about 0xc2x0 C. while the same is in said reaction zone, whereby the isobutylene in the reaction admixture is caused to undergo polymerization to form a polyisobutylene product. A product stream comprising a low molecular weight, highly reactive polyisobutylene is then withdrawn from the reaction zone. The introduction of the feedstock into said reaction zone and the withdrawal of the product stream from the reaction zone are controlled such that the residence time of the isobutylene undergoing polymerization in the reaction zone is no greater than about 4 minutes. In accordance with the invention, it is possible to conduct the reaction so that the residence time is no greater than about 3 minutes, no greater than about 2 minutes, no greater than about 1 minute, and ideally, even less than 1 minute.
In accordance with the concepts and principles of the invention, the process may be conducted in a manner such that the polyisobutylene thus produced has a number average molecular weight in the range of from about 350 to about 5000, in the range of from about 600 to about 4000, in the range of from about 700 to about 3000, in the range of from about 800 to about 2000, and ideally in the range of from about 950 to about 1050. In accordance with the invention, it is possible to so control the process that a particular molecular weight, such as for example, a number average molecular weight of about 1000, may be achieved.
A major purpose of the invention is to provide a process which may be controlled sufficiently to insure the production of a polyisobutylene product having a vinylidene content of at least about 70%. More preferably the PEB product may have a vinylidene content of at least about 80%. Vinylidene contents of at least about 90% may also be achieved through the use of the invention.
The complexing agent used to complex with the BF3 catalyst may desirably be an alcohol, and preferably may be a primary alcohol. More preferably the complexing agent may comprise a C1-C8 primary alcohol and ideally may be methanol.
To achieve the desired results of the invention, the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 5:1. Preferably the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 2:1. Even more preferably the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 1:1, and ideally, the molar ratio of BF3 to complexing agent in the complex may be approximately 1:1.
According to the principles and concepts of the invention, it is preferred that from about 0.1 to about 10 millimoles of BF3 may be introduced into the reaction admixture with the catalyst composition for each mole of isobutylene introduced into the admixture in the feedstock. Even more preferably, from about 0.5 to about 2 millimoles of BF3 may be introduced into the reaction admixture with said catalyst composition for each mole of isobutylene introduced into the admixture in the feedstock.
The invention provides a process whereby the polydispersity of said polyisobutylene may be no more than about 2.0, and desirably may be no more than about 1.65. Ideally, the polydispersity may be in the range of from about 1.3 to about 1.5.
In accordance with one preferred aspect of the invention, the reaction zone may comprise a loop reactor wherein the reaction admixture is continuously recirculated at a first volumetric flow rate, and said feedstock and said catalyst composition are continuously introduced at a combined second volumetric flow rate. The ratio of said first volumetric flow rate to said second volumetric flow rate may desirably range from about 20:1 to about 50:1, may preferably range from about 25:1 to about 40:1 and ideally may range from about 28:1 to about 35:1. In order to achieve the benefits of the invention, the ratio of said first volumetric flow rate to said second volumetric flow rate may preferably be such that the concentrations of ingredients in the reaction admixture remain essentially constant and/or such that essentially isothermal conditions are established and maintained in said reaction admixture.
The feedstock and the catalyst composition may be premixed and introduced into the reaction zone together as a single stream at said second volumetric flow rate. Alternatively, the feedstock and the catalyst composition may be introduced into the reaction zone separately as two respective streams, the flow rates of which together add up to said second volumetric flow rate.
To achieve the desired results of the invention, the reactor configuration, the properties of the reaction mixture, and the first volumetric flow rate may be such that turbulent flow is maintained in said reaction zone. In particular, the system may be such that a Reynolds number of at least about 2000 is achieved and maintained in said reaction zone. The system may also be such that a heat transfer coefficient (U) of at least about 50 Btu/min ft2 xc2x0 F. is achieved and maintained in said reaction zone. To this end, the reactor may preferably be the tube side of a shell-and-tube heat exchanger.
In further accordance with the concepts and principles of the invention, the feed stock may generally comprise at least about 30% by weight of isobutylene, with the remainder being non-reactive hydrocarbon diluents.
In a more specific sense, the invention may provide a liquid phase polymerization process for preparing polyisobutylene having a number average molecular weight in the range of from about 500 to about 5000 and a vinylidene content of at least 70%. The process may comprise providing both a feedstock comprising isobutylene and a separate catalyst composition made up of a complex of BF3 and a C1 to C8 primary alcohol. The molar ratio of BF3 to alcohol in said complex may desirably be in the range of from about 0.5:1 to about 2:1. The feedstock and the catalyst composition may be introduced separately or together as a single stream into a residual reaction mixture in a reaction zone, and the residual reaction mixture, the feedstock and the catalyst composition may be intimately intermixed to present an intimately intermixed reaction admixture in said reaction zone. The introduction of the catalyst complex into the reaction admixture may preferably be controlled so that about 0.1 to about 10 millimoles of BF3 are introduced for each mole of isobutylene introduced with the feedstock. The intimately intermixed condition of the reaction admixture should preferably be maintained and the temperature thereof kept at about 0xc2x0 C. or above while the admixture is in the reaction zone, whereby the isobutylene in the admixture undergoes polymerization to form said polyisobutylene. Thereafter, a product stream comprising the polyisobutylene product may be withdrawn from the reaction zone. The introduction of said feedstock into the reaction zone and the withdrawal of the product stream from the reaction zone may preferably be such that the residence time of the isobutylene undergoing polymerization in the reaction zone is no greater than about 4 minutes.
Even more desirably, the invention provides a liquid phase polymerization process for preparing polyisobutylene having a number average molecular weight in the range of from about 950 to about 1050, a polydispersity within the range of from about 1.3 to about 1.5, and a vinylidene content of at least about 80%. In accordance with this preferred aspect of the invention, the process comprises providing both a feedstock made up of at least about 40% by weight isobutylene and a separate catalyst composition made up of a complex of BF3 and methanol, wherein the molar ratio of BF3 to methanol in the complex ranges from about 0.5:1 to about 1:1. The feedstock and the catalyst composition are introduced either separately or together into a residual reaction mixture in a reaction zone. The residual reaction mixture, the feedstock and the catalyst composition are intimately intermixed by turbulent flow within said reaction zone, whereby an intimately intermixed reaction admixture is present in the reaction zone. Preferably, the catalyst complex is introduced into the reaction admixture at a rate such that about 0.5 to about 2 millimoles of BF3 are introduced for each mole of isobutylene introduced in the feedstock. The intimately intermixed condition of the reaction admixture is maintained and the temperature thereof is kept at about 0xc2x0 C. or more while the same is in said reaction zone, whereby the isobutylene therein is caused to undergo polymerization to form said polyisobutylene. A product stream comprising said polyisobutylene is withdrawn from said reaction zone. In accordance with the invention, the introduction of feedstock into the reaction zone and the withdrawal of product stream therefrom are controlled such that the residence time of the isobutylene undergoing polymerization in the reaction zone is within the range of from about 45 to about 90 seconds.